In the construction of a laminating machine which is to operate according to the double belt principle for the production of a pressure across a flat plane upon an area of a continuously moving panel of material, one is faced with the task of minimizing the friction forces occurring between the moving flexible steel belts and the stationary supporting structure which absorbs the reaction forces. Essentially two measures have become known as a solution to this problem: the arrangement of rolling elements between the steel belt and the supporting structure; and the arrangement of outwardly sealed pressure chambers filled with fluid pressure medium at the same locations. Some other, different, attempts at solving the problem have not achieved any significant acceptance in industry.
In the prior art solution proposals employing the arrangement of rolling elements, e.g. German offenlegungsschriften [Laid-open applications] Nos. 2,058,820, 2,343,437 and 2,215,618 and German Auslegeschriften [Published Applications] Nos. 2,157,746 and 1,004,368, it has been found difficult to keep short, or to sufficiently support, the belt region between the tangent contact point at the guide rollers at which the steel belts come into contact with or leave the guide rollers, respectively, and the reaction zone in which pressure is exerted on the backside of the belt.
This so-called dangerous entrance zone creates considerable limitations in use, depending on the material to be processed, for example higher belt temperatures for the manufacture of laminates of paper panels saturated with aminoplasts. Since no pressure can be exerted on the panel of material in the dangerous entrance zone, the saturating resins condense too early and the surfaces can no longer be compressed without pores in the subsequent reaction zone.
In prior art arrangements utilizing rod-shaped rollers which extended over the entire width of the belt, as disclosed in French Pat. No. 1,469,225 and Austrian Pat. No. 176,349, the rollers were to be guided outside of the pressure load zone, or several in juxtaposition within the pressure load zone, by means of sprocket chains whose individual links connected the pin-shaped ends of the rollers and kept them spaced apart. A significant drawback of this arrangement is the danger of serious damage to the machine if only a single one of the many parts of such a chain breaks and is crushed between the rolls.
In the case of panels of material which require extensive compression, such as, e.g., randomly distributed chips, their tendency to spring back is annoying, especially in combination with the fact that, for such applications in particular, long dangerous entrance zones are characteristic of all prior art solutions. This is the case for the systems disclosed in German Offenlegungsschriften Nos. 2,058,820 and 2,205,575, which are mentioned in this connection only to aid in understanding the nature of the difficulty.
Generally, rolling element belts and rolling element chains constitute known solutions to the problem of reducing friction between the moving pressing belt and the stationary supporting structure of such a machine. In particular, German Offenlegunsgschrift No. 2,215,618 makes suggestions to overcome the problems that occur. This publication also does not recognize the problem of a long entrance zone. Moreover, it presents no suggestions for reliably maintaining uniform spacing between the rod-shaped rolling elements, except for the already known technique of providing lateral guide members in the form of a chain. The same applies for French Pat. No. 1,469,225 and Swiss Pat. No. 327,433. Although this Swiss patent discloses a way of avoiding the dangerous entrance zone which, according to the descriptive text, has obviously not been recognized as such, it provides no teaching, except for a mention of the sprocket chain, of how to obtain reliable and wear-free operation with minimum supporting widths.